1. Field of the Invention
The present invention relates to a keyless entry apparatus that performs predetermined control such as locking and unlocking of doors of a vehicle by performing communication between a vehicle-side device and a portable device.
2. Description of the Related Art
A smart keyless entry apparatus in which wireless communication is performed between a vehicle-side device provided in a vehicle and a portable device carried by a user, and a door of the vehicle is locked or unlocked on the basis of this communication has been proposed (for example, Japanese Unexamined Patent Application Publication No. 2010-181295). In this smart keyless entry apparatus, the vehicle-side device includes a plurality of transmission antennas provided in respective places on the vehicle, and periodically transmits a start-up signal to the portable device to start up the portable device from a sleep state. The vehicle-side device transmits a measurement signal from each transmission antenna after a predetermined time elapses from the transmission of the start-up signal. The portable device that has started up then calculates a distance between the portable device and the vehicle-side device on the basis of a reception intensity of the measurement signal transmitted from the vehicle-side device, transmits distance data to the vehicle-side device, and enters a sleep mode until the portable device receives a next start-up signal. Accordingly, a distance between the vehicle and the portable device is calculated in a predetermined time period, and control of locking and unlocking of a door of the vehicle is performed according to a result of the calculation.
However, in a smart keyless entry apparatus of the related art, in a case in which a user carries a smartphone or another information device, a portable device receives radio waves generated by the information device, in addition to a start-up signal or a measurement signal transmitted from a vehicle-side device. Therefore, the start-up signal transmitted from the vehicle-side device may be buried in noise signals other than such a signal and may not be able to be discriminated from these. Accordingly, the portable device cannot be started up. Here, since the start-up signal has a complex signal waveform including information unlike a measurement signal having a simple waveform, the start-up signal is easily influenced by a noise signal. In a case in which the start-up signal is buried in noise signals, a signal is not returned from the portable device to the vehicle-side device. Accordingly, there is a problem in that the vehicle-side device erroneously determines that the portable device is at a position away from the vehicle regardless of an actual position of the portable device, a door is locked though a user is near the vehicle, and the door cannot be unlocked though the user is approaching.